1. Field of the Invention
The invention relates to fueling systems for vehicles, and, in particular, to a compressed gas vehicle fueling system installed in the vehicle, including electric power and low pressure gas connection means for coupling to electric and gas terminals outside the vehicle, enabling storage of a gaseous fuel supply on board the vehicle. The fueling system includes, in a compressed gas powered vehicle, a gas compressor operable to fill a pressurized gas storage system in the vehicle and an inlet that connects with a valved low-pressure gas line. The compressor is preferably a multi-stage compressor, with at least two, and preferably four stages, powered by standard domestic ac electrical power and in conjunction with the gas storage system can load sufficient fuel from a low pressure domestic natural gas line to power an automobile or similar vehicle over a typical operating range as needed to travel between locations at which natural gas supplies are conveniently available.
2. Prior Art
Gasoline and diesel fuels are relatively dirty in that they contain a substantial proportion of complex hydrocarbons as compared to other combustible fuels, as well as gum forming compounds that can clog fuel systems, and hydrogen sulfide and thiols (mercaptans) that are offensive to humans and corrosive to engine parts. Burning such fuels in an internal combustion engine or the like typically cracks hydrocarbon compounds in the fuel without completely oxidizing them. The result is various forms of encapsulating hydrocarbons, soot and the like, which together with other compounds are emitted in the exhaust, build up on engine pans, or otherwise contribute to the pollution of the environment. Petroleum is also an increasingly scarce resource.
By comparison, natural gas is a highly desirable fuel, especially based upon its performance for internal combustion piston engines. It is generally more available than petroleum fuels, and is widely distributed to stationary domestic installations as a preferred source of energy for appliances, heaters and the like. On the basis of cost per joule of heat energy, natural gas may be the least expensive fuel available in a given area.
Natural gas performs well in piston engines. Its high antiknock qualities permit design of highly efficient, high compression engines. The dry, sulfur-free form readily available from pipelines is an extremely clean fuel that bums cleanly in engines, producing minimal engine deposits and little or no corrosion of engine pans. However, because natural gas is a gaseous fuel it cannot be stored in conventional liquid fuel tanks. Thus its use as engine fuel is generally in connection with stationary installations, such as engines that power heavy duty compressors or drive generators in central power stations.
It has been attempted to use natural gas as a vehicle fuel, storing a quantity of gas at high pressure on board the vehicle. A substantial quantity of gas is needed to operate over a reasonable range between fillings. Vehicles powered by compressed natural gas require a storage system for the gas under pressure, such as a gas cylinder array. The gas is typically stored in a multi-cylinder array at a pressure of about 3000-3200 psi when fully charged, providing a typical operating range of about 100 miles or more, after which the cylinder array needs to be recharged. This range is adequate for many people, but requires that the storage system be refilled more frequently than a typical gasoline vehicle, for example on a daily basis.
To recharge the cylinder array, the vehicle is brought to a fueling station that can charge a cylinder array at high pressure in 5 to 15 minutes. Any more than 30 minutes is generally considered impractical. Fleet operators have invested in facilities for high-pressure charging of natural gas cylinders at their base of operations, such that each vehicle in a fleet (e.g., of taxicabs or delivery trucks) can be filled each day. A facility of this type may require a high volume and/or high pressure hookup to a gas pipeline, and means to pump the gas at sufficient pressure and capacity to serve the fleet.
The number of existing natural gas filling stations is limited. This is due not only to the limitation on the number of natural gas vehicles in existence, but also to the relatively large investment in a facility capable of extracting an adequate volume of gas from a pipeline or other source, pressurizing the gas and delivering it to meet reasonable time and quantity expectations. Facilities capable of high pressure storage and delivery, such as those used by commercial fleet operators, may be highly regulated or even prohibited by local zoning or building codes. They can be dangerous to operate and expensive to install.
On the other hand, natural gas is currently available at millions of residential and commercial sites to which it is generally delivered by underground pipes for powering heating and cooking appliances and the like. This gas is delivered at very low pressure, capable of delivering adequate energy for appliances. The typical input gas pressure is a minimum of six inches water column. The maximum pressure is 5 psig. A standard flow rate is 1.5 SCFM (at 100.degree. F. ambient). The delivery technique is generally considered safe, even though leaks result in fires or explosions occasionally. It is possible to equip a residence or the like with pressurized storage tanks and means to compress natural gas from the pipeline for storage in the tanks. However, it would not be safe to provide such equipment in residences, effectively attempting to provide a plurality of small scale filling stations, each capable of compressing, storing and delivering natural gas for filling vehicle tanks on demand.
Thus, notwithstanding its favorable combustion characteristics, natural gas remains an inconvenient fuel for typical consumers and operators of individual vehicles. The danger, expense and inconvenience associated with fueling facilities has severely inhibited the development and use of compressed natural gas as a vehicle fuel. There is a need for a more convenient system for charging storage cylinders in vehicles powered by natural gas, that takes advantage of the availability of the fuel to individual vehicle operators, but is not characterized by the danger and inconvenience of high pressure storage and delivery facilities.